1. Field of the Invention
The present invention relates to a base station transceiver in a CDMA (Code Division Multiple Access) mobile communication system and, more particularly, to a base station transceiver in a CDMA mobile communication system configured to have a separate hardware component for performing only a Viterbi decoding apart from a single hardware H/W that performs a composite function of modulation/demodulation and Viterbi encoding/decoding, thereby facilitating a decoding of demodulated signals received from multiple users.
2. Description of the Related Art
A base station transceiver (hereinafter, referred to as “BTS”) in a CDMA digital mobile communication system communicates data and voice signals with mobile stations in a wireless way, controls mobile stations (e.g., PCS phones, DCS phones) to monitor speech quality, and connects a base station controller to the mobile stations linked to each other with wires. That is, the BTS located between the mobile stations and the base station controller matches radio channels and performs important functions related to the radio channels. Here, the important functions concerning the radio channels may include allocation and control of forward power for CDMA frequencies, channels and frame option sources, processing of originating and terminating calls, processing of soft and hard handoff call signals, reception and control of GPS time information and application of system time information into the mobile stations and base station.
Also, the BTS involves communication of radio signals over pilot channels, sync channels, access channels, paging channels and traffic channels, application of routing from the base station controller for traffic and control information, detection of errors in the BTS, and collection and report of statistic information.
Now, a description will be made as to the BTS in the conventional digital mobile communication system performing the afore-mentioned functions with reference to the accompanying drawings.
FIG. 1 is a block diagram illustrating the BTS in the mobile communication system according to the prior art.
Referring to FIG. 1, the BTS 20 includes a BTS control processor 21 for entirely operating and controlling the BTS 20; a BTS network matching section (BTS interconnection network) 22 for performing a packet router between the BTS 20 and the base station controller 10 via a line E1 or T1 and interfacing HDLC (High-Level Data Link Control) packet data between the processors in the BTS 20; a time and frequency unit 23 for generating a reference frequency and a timing sync signals to acquire synchronization of the respective processors in the BTS 20 and timing synchronization with neighboring BTS's; a digital signal processor 24 for modulating/demodulating data and voice signals communicated via CDMA channels; and an RF (Radio Frequency) signal processor 25 for converting an RF signal received from the mobile stations to an IF (Intermediate Frequency) signal, transmitting the IF signal to the digital signal processor 24, converting the IF signal received from the digital signal processor 24 to the RF signal and amplifying the RF signal to a predetermined level for spatial distribution.
First, in the conventional CDMA BTS as constructed above, the BTS network matching section 22 provides interface with the base station controller 10 and an internal communication channel of the base station controller 10 by way of a packet router.
The base station controller 21 entirely controls the BTS 20 to perform an adequate operation and downloads related software during an initial operation of the BTS 20.
The digital signal processor 24, which is a unit for processing data and voice signals received from or transmitted to the individual mobile stations, i.e., performing modulation, demodulation, Viterbi encoding and Viterbi decoding, processes all signals related to the CDMA system. Thus the digital signal processor 24 performs quite different operations from that of the BTS's in other communication systems, e.g., AMPS or TDMA (Time Division Multiple Access) BTS's.
The RF signal processor 25 converts the data and voice signals modulated at the digital signal processor 24 to an RF frequency, which is then transmitted to the mobile stations. The RF signal processor 25 also demodulates the data and voice signals received from the mobile stations into digital signals to be transmitted to the digital signal processor 24.
The time and frequency unit 23 receives a reference time necessary to the BTS 20 by way of GPS and applies the reference time to the BTS 20, so that all units in the BTS 20 acquire synchronization with GPS time and share the same timing.
To sum up, the above-described base station in the CDMA mobile communication system according to prior art includes an RF processor, an IF processor, a modem, a Viterbi encoder/decoder and a control processor.
The modem and the Viterbi encoder/decoder are provided in a single hardware circuit pack, and one channel element, i.e., one modulator, demodulator or Viterbi decoder accommodates only one user. Thus there is a need of a plurality of channel elements in order to accommodate multiple users. That is, the conventional base station transceiver involves some problems in that there must be provided a plurality of hardware circuit packs including the Viterbi decoders and that, when required, the users and sectors, i.e., α, β and γ sectors must be increased in the units of channel element.
In addition, the Viterbi decoder has a capacity of no more than 144 Kbps even though there is a need of providing data and video services up to 144 Kbps with the advent of IMT-2000 (International Mobile Tele-communication) system, that is, the second-generation integrated radio communication service in the land and satellite environments supporting multimedia services of voice, high-speed data and image and global roaming. It is thus required to use a turbo decoder having a high decoding efficiency in order to provide high-speed services of greater than 144 Kbps. That is, there is required to substitute the Viterbi decoder with a turbo decoder in order to support a data service of higher than 144 Kbps with a modulator, demodulator and a Viterbi decoder in one hardware circuit pack, which incurs a serious problem involving an entire modification of the hardware circuit pack. Also, signals from multiple users are combined in the analog form and thus accurate synchronization is hard to acquire in the case of modulating the composite analog signals at a high chip rate such as in the IMT-2000 system. Furthermore, it is difficult to utilize the hardware efficiently because both the forward and reverse channels are allocated irrespective of the characteristics of the traffic channel.